1. Field of the Invention
The invention relates to a catheter having enhanced pressure sensing capabilities. More particularly, the invention relates to a balloon catheter having a micromanometer connected to the catheter and also a fluid-filled transducer system for adjusting micromanometer pressure measurements.
2. Description of the Prior Art
A key function of many catheters is that of continuously monitoring blood pressure. In many cases, this monitoring must be performed with accurate measurement of high frequency components. For example, reliable detection of the dicrotic notch of the aortic blood pressure waveform typically requires a pressure signal having a bandwidth of 15 Hz or better. Detection of the dicrotic notch is generally used for the inflation/deflation timing of an intra-aortic balloon (xe2x80x9cIABxe2x80x9d) catheter.
Conventional invasive pressure monitoring is performed with low-cost fluid-filled transducers. A typical disposable monitoring kit, inclusive of all tubing, a continuous flush device, and a pre-calibrated transducer is very affordable. Unfortunately, these systems have several drawbacks. One major drawback is that bubbles or clots in the monitoring lines can reduce the frequency response of the system to a level below 15 Hz, creating an xe2x80x9coverdampedxe2x80x9d condition. In other cases, the characteristics of the catheter and tubing can result in xe2x80x9cringingxe2x80x9d, which is associated with an underdamped condition. Furthermore, fluid-filled catheters can suffer from xe2x80x9ccatheter whipxe2x80x9d (motion artifact), which is manifested as one or more high frequency deflections in the pressure signal. These problems can degrade the usefulness of the signal in applications such as intra-aortic balloon pumping (IABP). In particular, it is difficult, if not impossible, to automatically provide optimal timing of IABP using a pressure signal with a frequency response below 15 Hz, or using signals with ringing or whip artifacts that mimic the physiologic dicrotic notch.
Another means for monitoring blood pressure is to use a micromanometer, such as marketed by companies such as Millar, Endosonics, and Radi. See U.S. Pat. Nos. 5,431,628 and 5,902,248, herein incorporated by reference. These devices can have excellent frequency responses, with system bandwidths greater that 200 Hz. They are not subject to the negative effects of bubbles and catheter whip, and retain good performance even in the presence of small blood clots. Unfortunately, they are very expensive, prone to signal drift, and can suffer from electrical interference. A common source of electrical interference in the setting of IABP therapy is the use of electrosurgery. In this situation, it is desirable to maintain a reliable pressure signal with which to trigger the balloon, as the ECG signal which normally triggers IABP operation becomes completely unreliable. Conventional fluid-filled transducer systems are relatively immune from this type of interference.
If the above problems were solved, micromanometers could potentially be used in conjunction with IABP systems and other catheters to measure blood pressure. Attempts have been made to use micromanometers for IABP timing, see U.S. Pat. Nos. 3,585,983 and 4,733,652, herein incorporated by reference. These attempts proved to be unreliable, as the device may be damaged during insertion and is also prone to signal drift. To address the drift issue, U.S. Pat. No. 5,158,529, herein incorporated by reference, discloses a method for rezeroing the micromanometer by using the pressure from a partially filled balloon as it rests in the aorta. However, this method requires momentary interruption of IABP, which may be harmful to the critically ill patient.
While standard IAB catheters incorporating a fluid-filled transducer pressure measurement system or IAB catheters incorporating micromanometers may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.
Accordingly, there is a need for a reliable and affordable pressure monitoring approach that has high bandwidth pressure sensing, low signal drift, and freedom from electrosurgical interference. There is also a need to incorporate this technology into intra-aortic balloon catheters having small cross sectional profiles.
The invention is an IAB catheter system having enhanced blood pressure sensing capability. The IAB catheter has a micromanometer, or any high fidelity sensor, built into the tip of the IAB or connected to another part of the catheter, and a fluid-filled transducer kit connected to the y-fitting of the IAB. The IABP console, including a processor, continuously monitors and compares signals from both the micromanometer and the fluid-filled transducer. The signal from the micromanometer may be continuously displayed, and either continuously or intermittently adjusted for baseline drift by comparing it to that of the fluid-filled transducer. The adjustment is preferably made by comparing mean blood pressures as indicated by the two sources.
The IABP console could also monitor the micromanometer""s signal for the presence of electrosurgical interference, mechanical damage, or any other possible causes of signal error. If significant errors are detected, the system automatically reverts to the use of the signal from the fluid-filled transducer system. The system also allows the user to manually select the use of the fluid-filled transducer, in the event that electrosurgical interference was anticipated.
To the accomplishment of the above and related objects the invention may be embodied in the form illustrated in the accompanying drawings. Attention is called to the fact, however, that the drawings are illustrative only. Variations are contemplated as being part of the invention, limited only by the scope of the claims.